Lactase is an enzyme decomposes lactose into glucose and galactose. While lactose is present in a dairy product using milk beverage such as milk, lactase is present in the small intestine of most humans. Therefore, the lactose in the dairy product is decomposed into glucose and galactose in the small intestine. However, there are partly some humans in whom lactase does not act sufficiently, in which case lactose is not sufficiently decomposed and symptoms such as diarrhea and indigestion occur. Lactase is widely used for decomposing lactose in dairy products. Further, lactase is widely used also for improving the degree of sweetness of milk beverage and fermented milk, producing ice cream and milk jam, imparting a caramel color, for example, to coffee milk, and the like.
Such lactase is produced from yeasts, fungi, bacteria, or the like. In particular, lactase is produced by culturing yeasts such as Kluyveromyces lactis (K. lactis), Kluyveromyces fragilis (K. fragillis), and Kluyveromyces marxianus (K. marxianus). However, a lactase-containing composition derived from such a microorganism contains a small amount of proteases. It is known that protease which contaminates lactase decomposes milk protein, increases the off-flavor (unpleasant odor) of milk, and reduces the storage stability (Non Patent Literature 1 and Patent Literature 2).
It is reported that a reduction in the amount of protease which contaminates lactase can be achieved by binding lactase to a chromatographic resin such as an ion exchange resin and thereafter desorbing or eluting only the lactase (Patent Literatures 1 and 2).